In a gas turbine, hot gases of combustion flow from an annular array of combustors through a transition piece for flow along an annular hot gas path. Turbine stages are typically disposed along the hot gas path such that the hot gases of combustion flow from the transition piece through first-stage nozzles and buckets and through the nozzles and buckets of follow-on turbine stages. The turbine buckets may be secured to a plurality of turbine wheels comprising the turbine rotor, with each turbine wheel being mounted to the rotor shaft for rotation therewith.
A turbine bucket generally includes an airfoil extending radially upward from a substantially planar platform and a hollow shank portion extending radially downward from the platform. The shank portion may include a dovetail or other means to secure the bucket to a turbine wheel of the turbine rotor. In general, during operation of a gas turbine, the hot gases of combustion flowing from the combustors are generally over and around the airfoil of the turbine bucket. To protect the part from high temperatures, a bucket airfoil typically includes an airfoil cooling circuit configured to provide a cooling medium, such as air, throughout the airfoil in order to reduce the temperature differential between the pressure and suction sides of the airfoil. In addition, the airfoil may have a cooling scheme or arrangement for supplying air to the tip of the airfoil.
Currently, the tips of bucket airfoils are cooled using a series of straight film holes defined along the perimeter of the airfoil near the tip. Specifically, the film holes are drilled radially down and inward from the airfoil surface near the tip into the cooling circuit of the airfoil to permit air flowing through the cooling circuit to be directed up along the tip. However, it has been found that this cooling arrangement provides for less than optimal cooling for the bucket tip. Additionally, such a cooling arrangement requires the drilling of an excessive amount of film holes and also requires the use of an excessive amount of air.
Accordingly, a cooling arrangement for an airfoil of a turbine component which effectively cools portions of the airfoil, such as the airfoil tip, while reducing the amount of cooling holes and air required would be welcomed in the technology.